Measurement of rubella antibody by hemagglutination inhibition. II. Characteristics of an improved HAI test employing a new method for the removal of non-immunoglobulin HA inhibitors from serum.

Abstract

A method employing dextran sulfate and CaCl 2 (DS-C) for removing nonspecific inhibitors of rubella virus hemagglutinin from test sera has been described. Sera treated by this method were shown to be free of detectable inhibitor. No quantitative changes in IgG, IgA and IgM could be detected, nor was any qualitative change in IgG observed as a result of DS-C treatment. The hemagglutination-inhibition (HAI) test employing DS-C treated sera was shown to be a true measure of actual rubella antibody content, and 100% of the HAI titers determined on 47 paired sera were identical or equivalent (±1 dilution). Kaolin by comparison was shown to be an unreliable means of specifically removing non-immunoglobulin inhibitors. Kaolin failed to remove inhibitors completely from many sera, and it sometimes removed specific antibody from others. A modified heparin-MnCl 2 procedure was found to give erratic and unreliable results. The basis for these undesirable characteristics of the heparin-MnCl 2 method was explored and an improved heparin-MnCl 2 procedure was tried. This procedure gives reproducible and reliable results, but has the disadvantage that it fails to remove all traces of inhibitor from some sera, thus giving rise to false positive tests.